Questions and postings pertaining to the usage of ImageMagick regardless of the interface. This includes the command-line utilities, as well as the C and C++ APIs. Usage questions are like "How do I use ImageMagick to create drop shadows?".

(not interested in gamma at this point).
The range for these parameters is 0 to QuantumRange, or from 0 to 100%. "QuantumRange" being the maximum possible value according to pixel depth. For 8bit/channel RGB images (the usual), it would be 255.0.
It also says:

If a % sign is present anywhere in the string, both black and white points are percentages of the full color range.